Cash and Cash Equivalents - Additional Information (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 257,120,000	$ 35,345,000	$ 33,271,000
Cash in transit for credit and debit card transactions	3,500,000	$ 1,900,000
Restricted cash	$ 168,000
Restricted cash, asset, statement of financial position [extensible list]	us-gaap:OtherAssets